1. Field of the Invention
The invention relates to a process for fabricating a micro-optical lens, and in particular to a process for fabricating a micro-optical lens that can be fabricated in a usual manner as a process for manufacturing semiconductor so as to facilitate the integration of a micro-optical system or a micro-optoelectronic system.
2. Description of the Prior Art
Like common planar optical system, propagation of light in space within a planar micro-optical system or micro-optoelectronic system exhibits similarly problems of divergence, alignment of optical axis and the like. Further, the approach to the wavelength of the system due to the miniaturization of optical device yields crucial diffraction effect. For example, in an Edge-Emitting Laser Diode commonly used in a micro-photoelectric system, its active region 11 as shown in FIG. 1 has an elongated pore in the YZ section that produces a relatively greater divergent angle at distant field in Z-direction, which not only is not favor for propagation in space, but also results in a poor coupling efficiency with a waveguide (e.g., optical fiber). Under these circumstances, optical devices having focusing function or optical mode conversion (circularization of light bean) are frequently utilized to reduce loss.
The sub-module of an optical transceiver described in “PLC Hybrid Integration Technology and Its Application to Photonic Components”, IEEE Journal Of Selected Topics In Quantum Electronics, vol. 6, No. 1, 2000, pp. 4–13 used gradient-index light guide to modify mode of light beam and hence promote the coupling efficiency. However, this approach involves finer and more sophisticated processes, such as etching of gradient-index waveguide, laser specular etching, secondary epitaxy and the like. Furthermore, in this case, the gradient-index waveguide was attached directly on the optical output terminal of a light-emitting element (semiconductor laser) resulting into a concern on the yield rate. Moreover, U.S. Pat. No. 5,963,577 and 6,160,672 provided optical device (such as spherical lens, cylindrical lens and the like) on a substrate of a planar micro-photoelectric system to promote coupling efficiency. However, this approach used optical device of a size higher than several hundred micrometer that forced the system substrate to have a receptive slot having a corresponding size. This would invariably enlarges the dimension of the system substrate as well as the complexity of production. In addition, an optical device needs an anchorage mechanism (e.g., an adhesive) to strengthen the mechanical characteristics of the system. U.S. Pat. No. 5,420,722 disclosed a laser module wherein a micro-lens was loaded vertically at the light output end to correct the light mode. This module needed also an additional anchorage mechanism and the application of a single element should be cut after mounting the micro-lens. Further, in the micro-optical read/write head for light storage access disclosed in U.S. Pat. No. 5,646,928, desired optical devices such as, for example, Fresnel lens, beam splitter, reflector and the like were formed on a Si substrate through a semiconductor micro-electro-mechanical process, and were then raised up to form a micro-optical system with its light axis parallel to the substrate and at the same time afford an essential support. It is obviously, however, that, in addition to the complexity resided in their establishment, mechanical and thermal stabilities of this micro-system constituted main concerns in its application.
In U.S. Pat. Nos. 5,079,130; 5,225,935; 5,286,338; 5,298,366; 5,324,623′ and 6,249,034, processes for forming micro-lens by baking a photoresist at elevated temperature, and applications of said micro-lens were disclosed. However, since all of those micro-lenses were planar micro-lenses (with their light axis parallel to the substrate), they were not applicable directly in planar micro-optical or micro-photoelectric systems with their light axis parallel to their substrate. Nevertheless, smooth surfaces of these lenses generated through by means of the surface tension on the photoresist did afford an improvement on the coupling efficiency of the optical system.
Accordingly, it is obvious that conventional techniques have following disadvantages to be improved:    1. Complex manufacturing process.    2. Larger optical devices, and increase of the size of the system substrate are necessary for improving coupling efficiency.    3. They are not applicable directly in a planar micro-optical or micro-photoelectric systems with light axis parallel to the substrate.
In the integration of micro-lens and micro-optical system, most of them need anchorage or support.